A semiconductor device is manufactured by repeating a process in which a pattern formed on a photomask is transferred on a wafer by lithographic processing and etching processing. In such a manufacturing process, it is important to realize a high yield in an early stage and maintenance of stable operation of the manufacturing process. In order to realize them, it is essential to perform an in-line inspection of the wafer, analyze a found defect rapidly, and utilize it for investigation of a cause of a defect occurrence and a countermeasure against the defect occurrence. The automatic defect review technology and the classification technology will be the key to rapidly linking an inspection result with the countermeasure against the defect. In the automatic defect review technology, numerous defects detected are reviewed at high speed and in the classification technology, the defects are classified by occurrence causes. With the development of the miniaturization of the manufacturing process, a defect size, which affects the manufacturing yield of the semiconductor device, has also been miniaturized. As a result, it is difficult to perform a review with high resolution by an optical review device. Therefore, the review device of a scanning electron microscope (hereinafter sometimes abbreviated as a “review SEM”) type capable of reviewing at high speed with high resolution has been made into products.
Position information of the defect on a semiconductor wafer is obtained from the optical defect inspection device, etc. In the review SEM, work to find a problem in the manufacturing process is performed by capturing an image with higher magnification than the optical defect inspection device. For example, stage movement to the position of the defect is performed at high speed. The position of the defect is detected in a low magnification image mode of the SEM, and a center of the defect is imaged in a high magnification image mode of the SEM. Then, a high magnification image obtained in this high magnification image mode is analyzed, and classification work of the defect is performed.
With the development of the semiconductor device, a space part of a line-and-space structure has been etched deeper, and a deep groove structure has been formed. An amount of signal electrons generated from the space part in electron beam irradiation has been decreased. Therefore, it has gradually become difficult to observe the space part compared with a line part since a signal-to-noise ratio reduces at the space part. In addition, a hole structure has also been etched deeper, and a deep hole structure is formed. Similarly, it has gradually become difficult to observe by the scanning electron microscope.
One of methods to improve the signal-to-noise ratio at the space part is the method in which a gain of a photomultiplier tube is increased. However, by this method, gradation of brightness in the line part within a same sample image increases simultaneously, and thus, it is impossible to observe the line part since the line part is too bright. Therefore, an energy filter is used to relatively increase the gradation of the space part by suppressing secondary electrons which cover the greater part of the signal electrons of the line part. The energy filter is a high-pass filter capable of selecting the signal electrons according to kinetic energy of the signal electrons.
As described in PTL 1, the following method has been known. In the method, the signal electrons are passed through a metal mesh on which a voltage has been applied, a retarding electric field is formed for the signal electrons, and the signal electrons are selected.
In addition, as described in PTL 2, the following method has been known. In the method, an electrode is arranged in an objective lens, the voltage is applied to the electrode, the retarding electric field is formed for the signal electrons, and the signal electrons passed through are selected.